This document provides: (1) a summary in layman terms
of the scientific findings on the biological and human health risks associated with
ozone depletion; and (2) an explanation and perspective on the predicted impacts.

2. Background

Concern about the effect of chlorofluorocarbons (CFCs)
on the ozone layer were first raised in 1974 by Drs. Sherwood Rowland and Mario Molina.
They hypothesized that CFCs were able to persist in the atmosphere long enough to
diffuse upward into the stratosphere. Once there, intense solar radiation would break
them up, releasing reactive chlorine atoms which would then destroy ozone. Their
theory initially met with skepticism but mounting evidence and the discovery of the
Antarctic ozone hole in 1985 galvanized the interest of scientists and policy makers.

Subsequent research has indicated that CFCs, along with certain
other chemicals from our industrialized society, are in fact depleting ozone in the
stratosphere.

The problem with introducing chlorine atoms into the stratosphere
is that a sequence of chemical reactions occur that result in the destruction of
ozone and the regeneration of the original chlorine atoms. In other words, the chlorine
atoms are not initially used up by the reaction. Rather, they are regenerated by
the reaction and therefore are capable of reacting with ozone over and over again.
Each chlorine atom can destroy over 100,000 ozone molecules before it ultimately
returns to the troposphere as hydrochloric acid and is removed during rain storms.

Relatively recently, human activities have introduced large
quantities of chlorine atoms into the atmosphere. Presently, each year, about 400,000
tons of reactive chlorine atoms are released by the breakdown of chlorofluorocarbon
(CFC) molecules and other compounds (80% man-made) in the stratosphere. The net effect
is to destroy ozone faster than it is naturally created.

Because ozone plays an important role in reducing the amount
of ultraviolet radiation that reaches the earth's surface, depletion of ozone brings
about an increase in ultraviolet radiation. Since UV radiation is readily absorbed
by living tissue, and since light at this wavelength has sufficient energy to break
chemical bonds, it can be injurious to both plants, animals and humans.

3. Solar Radiation & "Amplification
Factors"

Energy from the sun reaches the earth as infrared, visible,
and ultraviolet light. Ultraviolet light is biologically harmful above certain doses,
as demonstrated by sunburns. When discussing increases in harmful ultraviolet light
due to ozone depletion, it is helpful to distinguish between three different types
of ultraviolet light. These are: (1) ultraviolet A (UV-A) with wavelengths between
400 and 320 nanometers (nm)); (2) ultraviolet B (UV-B) with wavelengths from 320
to 290 nm; and (3) ultraviolet C (UV-C) with wavelengths between 290 and 190 nm.

UV-C is completely absorbed in the upper atmosphere by oxygen
and ozone. Only UV-A and UV-B reach the surface of the earth. UV-A is not affected
by changes in the levels of stratospheric ozone. UV-B is more biologically harmful
and is very sensitive to changes in stratospheric ozone.

The level of UV-B striking the earth varies by time of day,
season, cloudiness, and latitude. Stratospheric ozone also varies by season and is
especially dependent upon latitude. With the exception of the recent phenomena of
ozone holes over the poles, ozone is normally thinnest at the equator and thickest
at higher latitudes. See Figure 1.

Figure 1. Total column ozone global average
as a function of latitude. (From CIAP, 1975)

Because of these variations in UV-B and in the thickness of
the ozone layer, it necessary to average all of these factors globally to derive
an estimate of the change in the average exposure to UV due to ozone depletion.

Two other factors play a key role in predicting the biological
impact of ozone depletion:

Living things are much more sensitive to the shorter wavelengths
of UV-B.

The amount of UV-B radiation falls off rapidly at shorter
wavelengths

Because of these two factors, it would be misleading to estimate
biological impacts simply on the basis of the overall change in the radiant energy
of the UV-B radiation. Rather, it is necessary to predict the change in the quantity
of radiation at each wavelength and to weight the wavelengths according to their
physiological impact.

An example of the result of such weighting is graphically shown
in Figure 2. Without the weighting, it would appear in our example that the impact
of a 50% ozone depletion is small. For each different type of biological effect we
wish to predict, a different weighting function must be determined.

For these reasons, scientists use the term "percent change
in biologically damaging ultraviolet radiation" or %DUV for short, rather than
percent change in UV-B. %DUV is calculated using a weighting function as discussed
above, which takes into account the relative physiological impact of different UV-B
wavelengths. In epidemiological terms, %DUV is the "percent change in the physiologically
effective dose of UV-B".

This relationship between decreased ozone and increased dose
of physiologically effective UV-B is quantified by a "Physiological Amplification
Factor" (PAF). The PAF is defined as the ratio of the percent change in biologically
damaging ultraviolet radiation (%DUV) to the percent change in stratospheric ozone
(%O3).

PAF = %DUV / %O3

A second factor must be taken into account to finally calculate
the biological effect of a decrease in stratospheric ozone. Very often, the increase
in biological damage is not proportional to the increase in the "dose"
of a biologically damaging agent. For example, for skin cancer, our best evidence
is that a doubling of DUV results in at least a four-fold increase in the incidence
of skin cancer, rather than a simple doubling of the incidence of skin cancer. This
relationship between biological damage and increased dose of DUV is quantified by
a "Biological Amplification Factor" (BAF). The BAF is defined as the ratio
of the percent change in biological effect (%Eff) such as skin cancer, to the percent
change in DUV.

BAF = %Eff / %DUV

Finally, by multiplying the PAF by the BAF, we can calculate
the predicted percent increase in biological damage (%Eff) for each percent decrease
in ozone (%O3). This is simply called the "Radiation Amplification Factor"
(RAF).

RAF = PAF • BAF = %Eff / %O3

We will use this equation to determine the biological impact
of ozone depletion.

4. Effects on Humans

Some of the possible harmful effects of increased UV-B light
on humans include:

Immune inhibition

Skin deterioration

Cataracts

Skin cancer

4.1 Immune Inhibition

The effects of immune inhibition, skin deterioration and cataracts will not
be quantified here for the following reasons: Immune inhibition has been demonstrated
in laboratory animals but is not well quantified. Also, cancers other than skin cancer
do not increase at lower latitudes (where there is greater UV-B).

4.2 Skin deterioration

Skin deterioration due to sunlight is well documented but primarily
affects appearance and is not life-threatening.

4.3 Cataracts

Cataracts are a major cause of blindness in the world. In countries
with good medical facilities, surgery can prevent most cataracts from causing blindness.
Nevertheless, even in the U.S., cataracts are a leading cause of blindness. Every
year, about 50,000 Americans become blind. Worldwide, there are approximately 17
million people who are blind due to cataracts, accounting for more than 50% of the
blindness in the world (UNEP, 1994).

Exposure to UV-A (as opposed to UV-B) is believed to play a
significant role in the formation of cataracts and may also affect the immune system,
however the quantity of UV-A reaching the earth is not affected by depletion of ozone.
Nevertheless, a recent study (Taylor & McCarty, 1996) suggests that UV-B also
causes cataracts. However, there is presently inadequate information available on
the wavelength dependence of this effect and proper dose-response relationships.
Nevertheless, with some reasonable assumptions, estimates based on epidemiological
data can be produced. In 1994, the United Nations Environment Programme (UNEP, 1994)
sited estimates for the overall radiation amplification factor (RAF) for cataracts
of 0.3-0.6 and 0.5. This means that a 1% increase in ozone depletion would be expected
to result in approximately a 0.3 to 0.6% increase in the incidence of cataracts.
At this point in time, these estimates of the RAF have a high degree of uncertainty.

Assuming an RAF of 0.5 for cataracts, a sustained 10% increase
in ozone depletion would eventually bring about an increase of 850,000 blind persons
(van der Leun and de Gruijl, 1993). Since cataract induced blindness mostly occurs
in the later decades of life, the number of additional blind people would be roughly,
850,000 ÷ 25 or about 34,000 persons per year. Again, it should be kept in
mind that these estimates are highly uncertain.

4.4 Skin Cancer

There are two basic types of skin cancer: melanoma and non-melanoma.

Melanoma is the most serious form of skin cancer and is also
one of the fastest growing types of cancer in the U.S. If not caught in its early
stages, melanoma is often fatal. Melanoma cases in the U.S. have almost doubled in
the past two decades with 34,000 cases and 7,200 deaths in 1995 alone (Long et al.,
1996). This corresponds to a lifetime cancer risk factor of roughly one per 100 persons.

Non-melanoma skin cancer is the most common form of all cancers,
but has a low fatality rate. There were an estimated 800,000 cases and 2,100 deaths
in 1995 (Long et al., 1996) in the U.S. The lifetime cancer risk factor for non-melanoma
skin cancer in the U.S. is roughly one in five persons.

The evidence for UV being a causative factor in skin cancers
are as follows:

There is a striking increase with decreasing latitude (increasing
UV-B).

The cancers are most often found on areas of the body exposed
to the sun.

The incidence is higher in people with outdoor occupations,
and is higher in men that in women (although this is not the case for melanoma skin
cancer).

The incidence increases with age.

Conclusions are supported by animal studies.

In addition, there are additional suggestive factors:

Incidence has risen ten-fold since the 1930's corresponding
with the increase in "sunbathing" since that time although other factors
may play a role.

Incidence increases dramatically with lower levels of skin
pigmentation. When adjusted for population differences, White people have a 70 times
greater incidence than Black people and a 10 times greater incidence than Latin and
Asian peoples. Furthermore, when found in Black people, it is usually found on the
less pigmented parts of the body such as the soles and palms. Lastly, albino persons
are especially susceptible. The effects appear to be a direct result of shielding
of the DNA by melanin pigment.

The worldwide incidence of non-melanoma skin cancer can be
estimated. As stated above, the current incidence of non-melanoma skin cancer in
the U.S. is about 800,000 persons annually with a death rate of about 2,100 per year.
This is for a current population of about 270 million. The world population of White
people is about 1,095 million (N. America, Europe, and Russia). The Latin and Asian
population, with a susceptibility about 1/10th that of Whites, is 3,950
million (S. America, Asia). Blacks are for the most part not susceptible. This gives
a race-corrected estimated worldwide incidence for non-melanoma skin cancer of 5.4
million persons per year with a death rate of about 14,000. This number may be low
since it assumes the U.S. quality of treatment.

Estimation of Biological Amplification Factor for Skin Cancer:

A study in Norway (Henrikson, et al., 1988, 1990) divided
the country into 4 horizontal bands of latitude, which have appreciably different
amounts of UV radiation. Both non-melanoma and melanoma skin cancer statistics were
then plotted against UV dose. This study showed a BAF for both types of skin cancer
of about 2.0.

The National Research Council (NRC, 1979) used data from five
separate studies to plot both melanoma and non-melanoma cancer incidence among Whites
against latitudes from 25° north to 45° south. The studies showed remarked
uniformity of results. When combined with the observation that DUV is directly proportional
to latitude in this range, the results demonstrate a BAF of roughly 2.7 for both
types of skin cancer. It should be noted however, that this assumes that the amount
of skin exposed, amount of time spent in the sun, etc., do not vary across the plotted
latitudes (all of which are unlikely assumptions).

F. R. de Gruijl and colleagues (de Gruijl et al, 1993, 1994)
estimated the BAF for humans based on laboratory studies of the formation of tumors
in animals exposed to different wavelengths of UV radiation . Based on those studies,
they estimated BAFs for non-melanoma skin cancer only. The BAF for basal cell carcinoma
(BCC) and for squamous cell carcinoma (SCC) were estimated to be 1.4 +/- 0.4 and
2.5 +/- 0.7, respectively. Since basal cell carcinoma accounts for 80% of the non-melanoma
skin cancers, the average BAF is 1.6 +/- 0.5.

Estimation of Physiological Amplification Factor for
Skin Cancer:

Scientists believe that skin cancer is primarily the result
of UV radiation causing damage to the skin's DNA. For this reason, absent better
data, the UV-B absorption spectrum for DNA can provide a reasonable approximation
of the biologically effective dose of UV-B for skin cancer. Based on the DNA UV-B
absorption spectrum, the PAF for skin cancer is approximately 2.0.

Based on the above studies, we have conservatively assumed
a BAF of 2.0 and a PAF of 2.0 for non-melanoma skin cancers. The resulting Radiation
Amplification Factor for non-melanoma skin cancer due to ozone depletion is 4.0.
Similar numbers have been quoted by the popular press (Caldicott, 1992; Corson; 1990,
Gore, 1993).

It should also be noted that the estimates of the mean RAF
for non-melanoma skin cancer have been decreasing steadily over the past two decades:
6 in '71, 4 in '80, 3 in '89, 2.3 in '91 and 2.0 in '93 (van der Leun et al, 1993).

We have chosen a health-protective (i.e., conservative) RAF
of 4.0 to use in our estimation of health impacts in keeping the standard practice
of EPA and other agencies concerned with protection of public health, to typically
use a 90th percentile estimate, so that there is only a 10% chance that the risks
may actually be higher than what are projected (as opposed to a 50% chance).

The relationship between increased UV-B exposure and melanoma
skin cancer is less clear. For example, unlike non-melanoma skin cancers, the origin
of melanoma skin cancers appears to be linked with intermittent, intense exposures
(i.e., severe sunburns) and/or exposures in childhood (IARC, 1992). Also, the are
very few animal studies, and the one study we do have for a tropical fish indicates
a PAF much lower than 1.0.

As stated in the UNEP 1994 Assessment:

"It is conceivable that UV radiation may contribute in
various ways to the induction of melanomas, and that the specific mechanisms differ
in the two animal models. Although it is difficult to induce melanoma in mice by
UV irradiation, it can be done quite efficiently with exposure to chemical carcinogens,
and concomitant UV exposure can then promote the melanomagenesis.

How these experimental data should be extrapolated to humans
is, of course, very much an open question. CM in humans may well have a multifactorial
etiology. Although UV radiation is likely to play a dominant role, (e.g., initiating
precursor lesions during youth and suppressing immunity to the tumor cells as a result
of a sunburn in the final stage of tumor development), other factors may affect expression
of the UV effect."

For these reasons, we will not estimate an RAF for melanoma
skin cancer at this time.

5. Effect on Land Organisms

5.1 Cultivated Plants

Cultivated plants make up most of the world's food supply.
About 1,500 million tons of wheat, corn, and rice make up the staples of our planetary
diet. U.S. exports alone of these products are over $10 billion per year (Johnson,
1997). Therefore, even a small decrease in crop productivity from increased UV-B
would be of great economic significance.

A number of studies have been performed. The most recent results
suggest that 30-50% of all species are deleteriously affected by UV-B (Teramura and
Sullivan, 1994). Field studies have shown that there is a great variability in the
impact of UV-B between both species and varieties of the same species. The types
of impacts also vary greatly. They may include yield but also may involve changes
such as leaf size, photosynthesis rate, and resistance to diseases and insects.

Cucumbers are an example of the high sensitivity of some plants
to UV-B. Cucumber growth is only 50-60% as much at the equator as it is at a latitude
of 70° North.

Sugar beets, tomatoes, and mustard have also been sound to
be sensitive to UV-B levels, while peanuts, peas, potatoes, and sorghum are not sensitive
(NRC, 1979). With rice, corn, squash and soybeans, the response depends on the variety
(Tevini, 1993).

Based on such studies, it is clear that the environmental response
of plants to an increase in UV-B is likely to be complex. Small changes in leaf size
may increase the ability of weeds to grow around some crops. Small changes in resistance
to insects or disease, or in the length of the growing season, could cause large
changes in yield. The most likely thing to happen will be a change in the relative
population of the various species. Studies have shown that sometimes the crop wins
and sometimes the weeds win (Runeckles and Krupa, 1994).

Because of all these complicating factors, we have not attempted
to estimate potential crop loss from increased UV-B.

5.2 Wild Plants

By "wild plants", we mean essentially forest trees,
which accounts for 80% of the plant biomass productivity on earth.

One major concern with trees is that any reduction in their
productivity due to increased UV would affect their uptake of carbon dioxide from
the atmosphere. This would increase CO2 levels significantly. Thus, ozone
depletion could exacerbate the greenhouse effect. That in turn, could cause changes
to cloud cover, precipitation patterns, temperatures, and so on, which would impact
all life on this planet.

Of fifteen species of conifers, 7 were found to have been harmed
by UV, 5 were unharmed, and 3 were improved (Teramura, 1990, 1994). Loblolly pine,
which is grown in the Southeast U.S. for paper production, is one of the most sensitive
to UV radiation. Field studies have shown that after three years, an increase in
UV-B corresponding to a 25% decrease in ozone, caused a 17-19% loss of biomass in
three out of four seed types. Similar results were seen for a 16% equivalent ozone
reduction.

As in the case of the crop plants, the consequences of a small
ozone change on the world's natural plants is likely to be complex. We have not attempted
to estimate a cost at this time.

5.3 Animals

The direct effects of increased UV radiation on wild and domesticated
animals is not thought to be of great economic significance (NRC, 1982). First, most
animals are protected by fur or hair. Second, the few problems seen in cattle and
sheep are eye and nose cancers that are infrequent or too late to have an economic
impact. It should be noted however that indirect impacts, such as effects on their
habitat, or potentially, changes to the biosphere bought about by an exacerbated
greenhouse effect, could be more significant.

6. Effects on Marine Organisms
- Phytoplankton and Zooplankton

"Plankton" are the collection of small or microscopic
organisms, including tiny plants and animals, found in great numbers in fresh or
salt water at or near the surface. They are too small to swim any great distance;
thus, they drift with the currents and serve as food for fish and other larger organisms.

Phytoplankton, which are tiny aquatic plants, are particularly
important because they are the very base of the aquatic food chain:

Phytoplankton -> Krill -> all
higher aquatic species

Fish are highly dependent upon phytoplankton as a food source.
Since about 30% of all protein for human consumption comes from the sea, the human
food supply is also very dependent upon phytoplankton.

In addition, phytoplankton account for roughly half of the
worldwide uptake of carbon dioxide (CO2) from the atmosphere. Therefore,
any decrease in phytoplankton would have a major impact on global CO2
levels. For example, just a 10% loss would be equivalent to a doubling of all current
fossil fuel burning worldwide.

Pure water is transparent to ultraviolet radiation. It is the
presence of light scattering materials that cause attenuation. Typically, there is
about a 40% attenuation of UV light at 0.5 meters below the surface rising to an
80% attenuation at 1.5 meters (NRC, 1983).

Studies have found that phytoplankton are highly sensitive
to UV light and that even existing levels of UV radiation are highly toxic. In fact,
the population of phytoplankton at the surface of the ocean is only one fifth of
that 1.5 meters below the surface (Haeder, 1993). While phytoplankton appear to have
an ability to descend to lower depths during periods of high light intensity, they
respond only to visible light, not UV. Therefore, an increase in UV is not something
to which they would readily adapt (NCR, 1976).

Declines in phytoplankton production in Antarctic due to the
ozone hole have been documented (Smith et al., 1992). Other studies have shown that
shrimp, crab larvae, and anchovies are also sensitive to UV-B (Worrest, 1982).

One estimate (Haeder, 1993) is that a 16% loss of ozone would
lead to a 5% loss in plankton productivity, which would in turn lead to a 7% loss
in fish production. That is about 6 million tons of fish worth roughly $20 billion.

7. Issue of Adaptation to Higher
Levels of UV-B

Whether organisms could adapt to a higher level of UV-B radiation
remains a controversial issue. Studies have shown that repair mechanisms exist in
both plant, animal and human cells for UV-B insults.

However, studies on cells exposed to UV-B have also shown that
the genetic elimination of even one repair mechanism increases cell mortality by
one to two orders of magnitude and that elimination of two mechanisms increases cell
mortality by at least three orders of magnitude (Geise, 1976). Thus, it appears that
the existing cellular repair mechanisms are already taking care of 99% to 99.9% of
the UV damage, and the harmful effects that we see are due to the occasional failures
of the repair mechanisms. The conclusion is that adaptation to UV-B radiation may
already be largely optimized and any further improvement would take an extremely
long period of time.

Figure 3 shows the long term evolution of the atmosphere, including
the ozone layer, and the appearance of the major life forms over time. It also shows
that higher life forms did not appear until after the ozone layer was almost fully
developed, about 700 million years ago. But simple life developed 3 billion or more
years ago. In other words, life remained primitive for 2.3 billion years until the
ozone layer developed. It may be that if higher life could not develop and survive
without a highly developed ozone layer for 2.3 billion years, it just may not be
possible to do so.

Figure 3. Ozone, oxygen and appearance of major
life forms as a function of geologic time
(From R.P. Wayne, 1985)

8. Risk Perspective

The increased health risks due to ozone depletion are not meaningful
unless put into the context of other comparable health risks that we encounter on
an everyday basis.

Table 1 shows a comparison of several other types of common
radiation risks . Note that the incremental lifetime cancer risk due to medical x-rays
or even the potassium in our own bodies is about 30 in 100,000. More importantly,
non-melanoma skin cancer is rarely fatal while the types of cancers induced by radiation
from medical x-rays or potassium are often fatal.

Table 1. Comparison of
Several Common Radiation Risks (From Wilson and Crouch, 1987)

Action

Dose (mrem/year)

Cancers if all U.S. population exposed

Incremental lifetime cancer risk

Medical x-rays

40

1,100

3.09E-04

Radon gas

500

13,500

3.80E-03

Potassium in own body

30

1,000

2.81E-04

Cosmic radiation at sea level

40

1,100

3.09E-04

Cosmic radiation at Denver

65

1,800

5.06E-04

One transcontinental round trip by air

5

135

3.80E-05

Other common place risks to which we are exposed everyday are
shown in Table 2. Motor vehicle accidents, home accidents, and air pollution, have
individual lifetime death risks (as opposed to cancer risks) of approximately
2 in 100, 8 in 1,000, and 1 in 100, respectively.

Yet another way of looking at this is to consider the impact
of moving to a lower latitude. Since the amount of protective ozone in the stratosphere
is less at lower latitudes, the effects of ozone depletion can be compared to shifting
our exposure to the sun further south.

9. Conclusion

The potential effects of an increase in UV-B radiation on the
biosphere due to ozone depletion are very serious. It is fortunate the world governments
have united to restrict the production and use of chlorofluorocarbons. Many of the
worlds food staples would be adversely impacted by an increase in UV-B light. Because
of the adverse impact of UV-B light on the productivity of phytoplankton and zooplankton,
marine fisheries would be severely impacted.

Exposure to UV-B radiation is the principal cause of non-melanoma
skin cancers in humans. While infrequently fatal (0.26%), the incidence of non-melanoma
skin cancer is so high -- about 800,000 new cases in U.S. each year and an estimated
5.4 million cases worldwide -- that there are over 14,000 associated deaths each
year worldwide. Also, exposure to UV-B appears to also be a contributing factor in
the formation of cataracts which is the leading cause of blindness in the world.
For this reason, even modest increases in UV-B radiation due to ozone depletion would
be expected to bring about increased cases of skin cancer and blindness in the human
population.

In addition, a decrease in the productivity of forests and
phytoplankton due to increased UV-B would dramatically reduce the uptake of carbon
dioxide by plants. This would not only reduce oxygen production but would contribute
to global warming, with attendant changes in cloud cover, precipitation patterns,
temperatures, and so on, which would impact all life on this planet.

The complexity of interdependent effects makes it virtually
impossible to predict the full consequences of ozone depletion on the biosphere.
Fortunately, actions are already being taken by the world community to deal with
this problem.

de Gruijl, F.R., and J. C. van der Leun (1994) "Estimate
of the wavelength dependency of ultraviolet carcinogenesis in humans and its relevance
to the risk assessment of a stratospheric ozone depletion," Health Physics67, 317-323.